Exchange Server 2003 is the Microsoft messaging and collaboration server designed to help you communicate more effectively. Along with the rich client functionality provided by Microsoft Office Outlook 2003, Exchange Server 2003 offers:

Mobile, remote, and desktop e-mail access with state-of-the-art security and privacy
Lower cost of ownership through the services provided by Microsoft Windows Server 2003
High reliability and outstanding performance
E-mail-based collaboration
Easy upgrading, deployment, and administration

The benefits gained by Microsoft Exchange Server 2003 to all the Businesses are :

1. Enhanced security: To uphold the tenets of the Microsoft Trustworthy Computing initiative, Exchange Server 2003 and Windows Server 2003 share the goal to be secure by design, secure by default, and secure in deployment. Exchange Server 2003 protects your messaging environment better with:

Improved spam controls with Exchange Intelligent Message Filter and support for real-time block lists.
Secure/Multipurpose Internet Mail Extensions (S/MIME) support and automatic sign off after inactivity in Microsoft Outlook Web Access.
Updated Virus Scanning Application Programming Interface (VSAPI) and enhanced action and reporting through vendor software.

2. Reduced cost: Exchange Server 2003 offers better server consolidation with more mailboxes per server for Exchange Server 5.5 users:

Increased performance between Microsoft Outlook clients and Exchange Server 2003 increases productivity and enables Exchange Server mailbox server consolidation scenarios.
Support for four-node and eight-node clusters when used with Windows Server 2003 operating system, Enterprise Edition.
Improved performance on replication traffic when used with Windows Server 2003.

3. Increased productivity for IT staff: Administrators can save time and increase productivity with:

Single-seat administration for Exchange Server and infrastructure through Active Directory service.
Instantaneous, online snapshot and backup of Exchange Server databases and storage groups with the Microsoft Windows Server 2003 Volume Shadow Copy service and Exchange Server 2003.

4. Anywhere access: Enable your mobile workforce to stay connected:

Exchange ActiveSync provides direct synchronization between Windows Mobile–based Pocket PCs and Smart phones and other mobile devices such as the palm-One Treo 650 and enabled Motorola mobile phones. This capability reduces costs by eliminating the need for additional servers and special services.
Extensible HTML (XHTML) (Wireless Application Protocol [WAP] 2.x), compressed HTML (CHTML), and HTML browser-based devices and mobile devices that can browse Exchange Server 2003 mailboxes.
Ubiquitous client access using a single URL for all external client types such as Outlook, Outlook Web Access, and mobile devices.

5. Increased server availability and reliability: With the Windows Server 2003 operating system, Enterprise Edition, you get improved virtual memory management and four-node and eight-node node clustering, plus speedier mailbox recovery:

Improved cluster failover time
Improved public folder replication
Integrated Mailbox Recovery Center
Recovery Storage Group

6. Faster, easier upgrades and deployment: Exchange Server 2003 makes upgrading easier with:

More checks to ensure that your earlier environments have been correctly prepared before native Exchange Server 5.5 upgrades.
Active Directory Connector Wizard that automatically creates connection agreements between Exchange Server 5.5 and Active Directory.
Public folder migration and new administration tools.
Easier migration and co-existence using Lotus Notes and GroupWise connectors.

7. Immediate increase in user productivity: Integration improvements with next version of Microsoft Office Outlook 2003 and Outlook Web Access offer:

Greatly improved Outlook and Outlook Web Access performance that enables high productivity for mobile workers connecting over slow, latent, inconsistent network connections.
Increased security for Internet access from Outlook through remote procedure call over hypertext transfer protocol (RPC over HTTP) that reduces the need for a virtual private network (VPN) connection when used with the Windows Server 2003 operating system.
Improved Outlook Web Access interface and features offering a faster, richer, and more useful user experience.

8. Collaborative application development: Enable line-of-business applications and other programs to securely access Exchange Server data and to provide integrated workflow scenarios and Web services.